OK, mine runs decent, gets great mileage. Jetted right and no other mods,but every mod page I read says to drill out the hole in the slide to 1/8"

I understand a lighter spring will allow the main jet to come in earlier, but what exactly does drilling out the hole in the slide do for it?

(I have an extra slide - just thought I'd ask before I tinker with it)

 

It will make the slider react faster I do it in some cases FXR's FXD's the lighter bikes Most baggers probably wouldn't benefit this faster slider response

 

I have only heard of doing thatwhen fitting a carb conversion kit, such as a Dynojet. The jet kit includes a lighter spring and involves undoing the lean burn settings of the factory, to improve engine running. I have just fitted a Screaming Eagle air filter and Custom Chrome jetkit to my wife's Dyna andthe kitcame with the correct size of drill bit!

I am not sure what advantage the hole willgive on its own.

 

Drilling out the slidewill make the carb more responsive. The air lets venturi pressure up above the rubber diaphragm in the top of the carb. By making this hole bigger, air will get up there faster, making the slide move and down faster.
Also you could turn the air mixture screw counterclockwise 1/4 turn to make it richer. If you need any help with this let me know.

 

thanks,

I just couldn't see what it'd actually do... I read a lot about shimming the needle height also - but that's a no-brainer.

It's an '87 FLT with a stock '95 CV jetted 48/175 stock air cleaner. 50-53mpg just knocking around and44-47mpg at sustained high speed (interstate) so I think I'll leave it just like it is!

 

I agree, With your bike and riding style i dont think you would gain anything by drilling the slide... In my shop we did it on many bikes but it was most noticeable on the Sportsters.

 

Guild,
Drilling the hole bigger actually an air bleed that lets the air out of the area above the diaphragm. What opens the slide is the air that flows through the oval opening at the top of the front of the carb just above the throttle bore. Try it if you don't believe me. Take and blow into the oval opening and watch the slide open.

 

I used a 7/64 drill bit to enlarge the hole and used 2000 grit sand paper and smoothed it out. Mine has excellent throttle response. I'm surprised at 50 plus mpg around town with the 48 slowjet, must be the bagger gearing. My 92 fatboy 80" running 45/175 with a sportster needle pulls mid 40's. Just curious what needle are you running? Thanks Kent

 

Apologies for not getting back to this sooner...

I was running the needle that came with the used CV off a 95 Softtail. Jetted 45/165 with an N86E (leanest) I went to the 175 first, then added the 48. In all honesty, I was fooling myself into thinking that was good. The 48 was rich (but trimmed with the screw) and 175 was barely adequate at high speed.

So I did drill the spare slide and changed nothing else except for a mild chamfer job on the front edge of the slide. OH BOY! Talk about throttle response - I had no idea it had been so dogish for so long. Then I added a short spring (out of 44MM TC carb) and it ruined it. Way too much lift/air and all the jetting changes thereafter produced no satisfaction.

In the interim, I stumbled acrosss an HD Thunderslide Kit for cheap, complete with a used diaphragm. Actually, the slide/diaphram were the only used parts in the kit and it was complete. I installed all that and particularly was happy to get a new accelerator nozzle/check valve, as mine had been slobering too long.

So I ended up with 45/185, needle clip @ 3 and 2.5 on the mixture. I rode a good bit Sunday at 70 degrees and later at 3000 feet and 65 degrees. At interstate speeds (over 65 - under 75) I got 45.9 and at low speed 45 - 55mph some hills, and no traffic and got 55mpg. Bear in mind, that was extremely conservative on acceleration both conditions.

I ride more cooler weather than extremely hot, but think I still have a bit of tweaking yet to be tried because the major increase in throttle response seems to fade a slightly in higher air temps. But for now, I'm totally good with it!

And, in all fairness, I believe if I'd gone back with a stock spring and the originally drilled slide, certainly a richer needle and played with shims, I am confident that combination would have given me similar results concerning response and mileage. I may try it sometime later....

 

It sounds like you did a good job, the best cv carb setup I had was done by Wally Kerstetteer in Sunbury, Pennsylvania and it was a reasonable price.


http://www.harleydavcvcarbrebuild.com/

http://www.hotbikeweb.com/tech/0406h...pes/index.html